Large trees store up to half the above-ground biomass in tropical forests, reiterating their importance in buffering against climate change, finds a study published in Global Ecology and Biogeography.

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The research, which involved dozens of scientists from more than 40 institutions, is based on data from nearly 200,000 individual trees across 120 lowland rainforest sites in Africa, Asia, and Latin America. It found that carbon storage by big trees varies across tropical forest regions, but is substantial in all natural forests.

African rainforests, with an average of 418 tons of above-ground biomass per hectare, stored the most carbon. Big trees — defined as those measuring at least 70 cm in diameter at breast height — accounted for an average of 44 percent of African forests' biomass. Other research has suggested that the preponderance of large trees in African forests is due to the abundance of large herbivores, which suppress smaller trees.

Asia was second with an average of 393 tons, of which large trees accounted for 154 tons or 39 percent of total above ground carbon. Latin America averaged 288 tons per hectare, about a quarter of which occurred in large trees.

The findings emphasize the importance of big trees, which typically dominate old-growth forests.

"Big trees represent less than 5% of stems, but store up to 50% of tropical forest biomass," lead author Ferry Slik of China's Xishuangbanna Tropical Botanical Garden told mongabay.com. "This makes tropical forest biomass storage very vulnerable to global change, especially if droughts would become more frequent and intense."

Big trees also have important ecological functions, offering niche habitats for wildlife and providing abundant fruit, foliage, and flowers.

Yet big trees are particularly at risk due to their attractiveness to loggers, who typically target the largest and oldest trees in selective logging operations. Big trees are also especially vulnerable to ecosystem change, including drought, increased incidence of wildfires, edge effects, and disease, according to a 2012 paper published in the journal Science. Taken together, the new study adds urgency to calls to better protect old-growth forests for climate stabilization and conservation of biodiversity.

"Once lost, it takes hundreds of years to get these big trees back, so we'd better take good care of them," said Slik.